GEOL 104 Dinosaurs: A Natural History

Fall Semester 2016
Walking with Dinosaurs: Trace Fossil Analysis

Ichnology: the study of trace fossils.
Most dinosaur ichnologists concentrate on footprints and trackway analysis.

An individual footprint represents:

Footprints give direct information about the soft tissues of the bottom of the foot, and about the natural position of the toes.

Trackways, however, give even more data. By measuring the stride length, and estimating hip height, the speed of the dinosaur at the time of that trackway can be calculated. These data tend to show dinosaurs walking around at speeds comparable to modern large-bodied mammals.

However, trackways do have some problems:

Footprints and trackways can, however, reveal the presence of dinosaurs not yet known by body fossils (such as Middle Jurassic North American dinosaurs).

There is a whole discipline of ichnotaxonomy: the naming of trace fossils. However, it must be remembered that these are sedimentological entities, not biological entities: the same animal can produce tracks given entirely different ichnotaxonomic names if it is walking slowly or running; on soft mud or hard mud; if adult or juvenile; etc.

One interesting note: almost no dinosaur trace fossil shows tail drag marks: this was some of the first evidence that dinosaurs held their tails up above the ground.

Trace fossils can help us understand something about group behavior. A recent study of Alaksan hadrosaurs showed many individuals moving in the same direction at the same time (based on the similar quality of footprint preservation.) Additionally, by counting up the trackways of different sizes, it helped to give an estimate of the relative fraction of the herd of different growth stages.

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Last modified: 15 August 2016